The wastewater from an industry may be organic or inorganic in nature or a combination of both. In most cases, it contains toxic ingredients. The direct effect of wastewater pollution is to deplete, through the excessive organic load, the dissolved oxygen (D.O.) content of receiving waters to the point that the stream becomes incapable of exercising the self-purification processes. The deoxygenation may be high enough to destroy practically all fish and other aquatic life. Such polluted water may also cause sporadic outbreaks of water-borne diseases (Nandan and Raisuddin, 1996). The problem is compounded by the fact that solubility of oxygen in water is very low, less than 12 mg/l. This oxygen comes from two sources, viz. diffusion from the atmosphere at the air/water interface and as a by-product of photosynthesis. Photosynthetic organisms, such as plants and algae, produce oxygen when there is a sufficient light source. During times of insufficient light, these same organisms consume oxygen, resulting in the depletion of DO levels.
Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) are indices of the biologically degradable and chemically oxidizable fractions of the wastewater, respectively. These parameters are frequently used to define influent and effluent characteristics as also ensure the wastewater treatment efficiency. These are monitored regularly to give clearance to the discharge of the above wastewaters. Recalcitrant organic matter (ROM), which is presumed by some to be partly responsible for long-term sub-lethal toxicity in receiving waters (Labunska et al, 2001); is sometimes represented in terms of a lumped parameter, the COD. COD of the treated effluent is representative of the effectiveness of a treatment technique in its ability to remove the total organic material present in the influent.
BOD is the most widely used measure of the biodegradable organic content (Chee et al, 2000) and is usually expressed as the 5-day BOD at 20° C. (BOD5) (APHA, 1998). The determination involves the measurement of dissolved oxygen during the biochemical oxidation of organic mater by the microorganisms at a standard duration and temperature. Microbes oxidize organic matter to provide themselves with sufficient energy to enable them to synthesize the complex molecules such as proteins and polysaccharides, which are needed to build new cells (Sessa, 1979).
Pulp and paper industry is one of the most important point sources for BOD elevation in the receiving waters; more so because most pulp mills are situated near rivers. The treated effluent is representative of the effectiveness of a treatment technique in its ability to remove the total organic material present in the influent. The contributors to COD in biotreated effluents are not only the non-biodegradable recalcitrant organic matter, but also a certain amount of degradable organic matter, which has resisted biodegradation due to its existence in a state where it was not bioavailable (Konduru et al, 2001).
A recent internal survey within the pulp and paper industry has reported that the COD values of the wastewaters can be as high as 11000 mg/l (Thompson and Forster, 2003). Typical loadings of BOD, COD and solids in the pulp mill effluents depend significantly on:                nature and cleanliness of the stock        whether the pulp and paper mill is equipped with a chemical recovery facility        the bleaching sequences applied and        the efficiency of the chemical recovery plant, as much as 96% of the COD load can be removed from the pulp cooking liquor.        
The pollution load in terms of biological oxygen demand (BOD) from small paper mills is 2-5 times the pollution load from large paper mills equipped with soda recovery. Mills producing paperboard generate relatively lower volumes of wastewater (68-90 l/kg of product) with high BOD (72-82 kg/ton of product) and suspended solids (224-290 kg/ton) as compared to paper mills. Table 1 shows the mean range of concentrations of BOD, COD and SS normally measure in untreated pulp and paper mills.
TABLE 1Mean/Range of concentrations (mg/l) of BOD, COD and Suspended Solidsnormally measured in untreated pulp and paper mills.Mill SourceBODCODSSIntegrated pulp and paper mills160550230Paper mills160–1150310–1100015–3230Source: Murtedza Mohammed, 1995
Biological treatment gives the ideal solution to treatment of wastewaters as less sludge is produced as compared to chemical treatments. Lower daily running costs are also incurred. Conventional treatment technologies essentially involve aerobic biological treatment methods.
Researchers across the globe have tried to devise innovative methods for achieving maximum reduction in the BOD and COD loadings of pulp and paper mill wastes.
Although numerous studies have looked at ways to degrade or remove COD and BOD of the pulp and paper effluents, the problem remains (Arcand and Archibald, 1993). COD removal of up to 80% by Leptothrix ochracea, Pseudomonas multistreata and Flavobacterium ochracea, isolated from activated sludge (Srivastava et al, 1995) has been reported. Tarlan et al, 2002, reported the use of algae for removal of COD in the range of 55-60%, however, only after a period of 20 days of retention.
Belsare and Prasad, 1988 reported that the effluent from bagasse based pulp and paper mills, when treated with the white rot fungus, S. commune, was able to reduce the BOD and COD of the effluent. However, an additional C-source like sucrose was required for the same with a 2-day incubation period and a pH of 4-5. Many other workers have also reported the use of white rot fungi for reduction of BOD and COD load of such wastewaters, in addition to decolorization (Kirk et al, 1976; Eaton et al, 1980; Prasad and Joyce, 1991; Nagarathanamma et al, 1999).
Sharma and Bandopadyaya, 1991, reported that lignin is not easily biodegradable and hence counts for high COD/BOD ratio. They used an anaerobic filter for the treatment of pulp and paper mill waste and achieve a maximum COD removal of 84.38% for an influent concentration of 4182.5 mg/l. Anaerobic processes are often prescribed as the first pretreatment step for pulp and paper mill wastewaters with increased COD concentrations, in order to meet the corresponding effluent requirements (Babuna et al, 1998). According to them, the magnitude of inert fractions in treatment of effluents is more important than the kinetics of the biodegradable part of the influent COD. They described an anaerobic application basis of a newly developed method that identifies separately the soluble and particulate initial inert and residual products. It was concluded that with the mentioned wastewater sample, having a total COD of 13000 mg/l, it is not possible to achieve a lower COD value than 2230 mg/l, which is the sum of the initially inert soluble COD and the soluble residual microbial products under anaerobic conditions. Grover et al, 1999, reported the use of an anaerobic baffled reactor (ABR) and effect of different pH, temperatures, hydraulic retention times and organs loading rates on continuous anaerobic digestion of black liquor from pulp and paper mills. A maximum COD reduction of about 60% at an organic loading rate of 5 kg m−3d−1 at a hydraulic retention time of 2 days was recorded.
Ali and Sreekrishnan 2000, reported reduction of COD and AOX of black liquor and bleach plant effluent from an agroresidue based pulp and paper mill by anaerobic treatment. Addition of 1% w/v glucose however was a necessity as in its absence only about 31% of COD reduction could be achieved. Wagner and Nicell, 2001, reported the treatment of a foul condensate from kraft pulping with Horse Radish Peroxidase and hydrogen peroxide. Although, a total phenol reduction occurred, the overall COD removal was marginal.
Modifications in the bleaching sequence can lead to reducing the pollutant loading to levels lower than those normally found in the effluents of mills using the conventional bleaching sequence, CEHDED. E.g., when the chlorine delignification stage is preceded by oxygen treatment, the resulting color, BOD and COD levels were found to be 87%, 77% and 76% less than the levels recorded for CEDED (Muhammed, 1995). Certain studies seem to indicate that the residual color in pulp mill effluents may be linked with the recalcitrant COD. Kemeny and Banerjee, 1997 observed a correlation between the end-of-pipe COD and color, thereby suggesting that the residual color might be related to the organic component that is not removed during treatment.
Till date, the are almost no reports regarding the utilization of pure bacterial cultures for bringing down the COD and BOD of pulping effluent. The novelty of the present invention is the application of pure cultures of bacteria in the form of a specifically designed synergistic mixture; isolated from natural habitat, for removing COD and BOD of the pulp and paper wastewaters in an industrially and economically viable fashion.